An internal combustion engine includes an engine block defining a plurality of cylinders, with an injector located at each cylinder. Fuel injectors are fed by one or more, high or low pressure pumps, as is well known in the art of fuel injection systems. The use of the electronically controlled fuel injector has become widespread. This type of fuel injector is in communication with the engine controller, and the engine controller generates a command signal to demand the initiation of the injection event. In response to the command signal, a current driver connected to an injector supplies current. Because fuel injection control strategies are complex, sometimes a sensing element is used to provide a signal indicative of the injector current during fuel injection.
A control circuit monitors the current detected by the sensing element, and controls the current driver in accordance with the injection strategy. Monitoring the current through the sensing element allows, for example, detection of the current inflection that occurs as the injector opens. Further, for example, monitoring the injector current allows the use of an injection control strategy in which a full current drive is used to open the injector, but then a pulse width modulated drive signal is used to maintain the injector in the open state. Although the full strength drive signal is needed to open the injector, the pulse width modulated signal through the bulk of the injection event has been found to reduce power dissipation.
Many times, different injectors require slightly different control strategies in order to provide acceptable performance. For example, the inflection in the injector current that is known to indicate that the injector has opened may have different characteristics for different injectors. For example, voltage levels near the inflection point may vary from injector to injector, and particularly from manufacturer to manufacturer. Further, for example, due to the construction of the injector, different injectors may require different duty cycles for the pulse width modulated portion of the injector drive signal. In an existing fuel injection control systems and drive circuits, changing an injector means that the drive circuitry hardware must be modified so as to be suitable for the characteristics of the new injector. Further, aside from current detection, existing control systems do not have much functionality besides direct current sensing.
For the foregoing reasons, there is a need for a system for controlling a fuel injector that may be made to accommodate different injectors having different performance characteristics with less difficulty than the systems and drive circuits existing today, and that has added functionality compared to the existing systems.